In recent years, electronic devices, such as mobile phones, laptop computers, electronic notebooks, digital cameras, and game machines, generally have audio functions. A sound emitter such as a speaker and a buzzer, or a sound receiver such as a microphone, is disposed inside a housing of an electronic device having audio functions. An opening is provided in the housing of the electronic device at a position corresponding to the sound emitter or the sound receiver. Sounds are transmitted through the opening. In addition, in order to prevent foreign matters such as water droplets from entering the housing of the electronic device, a sound-transmitting membrane that allows passage of sounds and prevents passage of foreign matters is disposed so as to cover the opening.
A known sound-transmitting membrane is a porous plastic membrane produced by forming pores in a polytetrafluoroethylene (hereinafter, sometimes referred to as “PTFE”) film or an ultrahigh molecular weight polyethylene film (see Patent Literature 1).
Patent Literature 1 proposes a sound-transmitting membrane including a porous plastic membrane and a support bonded to the porous plastic membrane, in view of ease of secondary processing of the sound-transmitting membrane, such as cutting, punching, and bonding to a case. Nets, nonwoven fabrics, and woven fabrics are mentioned as examples of the support. Patent Literature 1 also proposes a sound-transmitting membrane including a porous plastic membrane and a support bonded to the porous plastic membrane and having a surface density within a predetermined range in order to prevent a decrease in the sound transmissibility of the sound-transmitting membrane.
Patent Literature 2 proposes a waterproof sound-transmitting membrane as a layered product composed of a plastic membrane and a support. Porous materials such as nets, foam rubbers, and sponge sheets, nonwoven fabrics, and woven fabrics, are mentioned as examples of the support.
Patent Literature 3 proposes an acoustic part having a waterproof filter (waterproof sound-transmitting membrane) attached to a housing so as to cover a sound-transmitting hole of the housing with an adhesive layer interposed between the filter and the housing.